Urinary excretion reflects lung deposition of aminoglycoside aerosols in cystic fibrosis

Using nebulization to deliver aminoglycosides may be of benefit in cystic fibrosis (CF) patients colonized by Pseudomonas aeruginosa. However, one problem with this route is the absence of clinical parameters allowing estimation of the mass of drug deposited in the lungs (MDL). The aim of this study was to assess whether aminoglycoside excretion in the urine reflects the MDL. Fourteen studies were performed in seven CF patients. Amikacin was mixed with albumin labelled with Tc-99m and nebulized with an ultrasonic nebulizer. The MDL was determined by the mass-balance technique. Urine was collected during the 24 h following inhalation and was assayed for amikacin by fluorescence polorization immunoassay (FPIA). The mean SEM MDL was 14.0 +/-2.2% of the nebulizer charge. The mean SEM amount of amikacin excreted in the urine was 20.9 +/-4.5 mg and correlated with the MDL (r=0.93; p=0.0001). There was, however, wide intersubject variability in both deposition and excretion in the urine. Monitoring excretion of aminoglycosides in the urine allows noninvasive estimation of the mass of drug deposited in the lung in cystic fibrosis patients, which might be useful to assess the dose-response relationship in groups of patients, but intersubject variability prevents its use for individual follow-up.